<?php

/* SVN FILE: $Id$ */
/**
 * SassScriptLexer class file.
 * @author      Chris Yates <chris.l.yates@gmail.com>
 * @copyright   Copyright (c) 2010 PBM Web Development
 * @license      http://phamlp.googlecode.com/files/license.txt
 * @package      PHamlP
 * @subpackage  Sass.script
 */
require_once('literals/SassBoolean.php');
require_once('literals/SassColour.php');
require_once('literals/SassNumber.php');
require_once('literals/SassString.php');
require_once('literals/SassList.php');
require_once('SassScriptFunction.php');
require_once('SassScriptOperation.php');
require_once('SassScriptVariable.php');

/**
 * SassScriptLexer class.
 * Lexes SassSCript into tokens for the parser.
 *
 * Implements a {@link http://en.wikipedia.org/wiki/Shunting-yard_algorithm Shunting-yard algorithm} to provide {@link http://en.wikipedia.org/wiki/Reverse_Polish_notation Reverse Polish notation} output.
 * @package      PHamlP
 * @subpackage  Sass.script
 */
class SassScriptLexer
{

    const MATCH_WHITESPACE = '/^\s+/';

    /**
     * Static holder for last instance of SassScriptLexer
     */
    static public $instance;

    /**
     * @var SassScriptParser the parser object
     */
    public $parser;

    /**
     * SassScriptLexer constructor.
     * @return SassScriptLexer
     */
    public function __construct($parser)
    {
        $this->parser = $parser;
        self::$instance = $this;
    }

    /**
     * Lex an expression into SassScript tokens.
     * @param string expression to lex
     * @param SassContext the context in which the expression is lexed
     * @return array tokens
     */
    public function lex($string, $context)
    {
        // if it's already lexed, just return it as-is
        if (is_object($string)) {
            return array($string);
        }
        if (is_array($string)) {
            return $string;
        }
        // whilst the string is not empty, split it into it's tokens.
        while ($string !== false) {
            if (($match = $this->isWhitespace($string)) !== false) {
                $tokens[] = null;
            } elseif (($match = SassScriptFunction::isa($string)) !== false) {
                preg_match(SassScriptFunction::MATCH_FUNC, $match, $matches);
                $args = array();
                foreach (SassScriptFunction::extractArgs($matches[SassScriptFunction::ARGS], false, $context) as $key => $expression) {
                    $args[$key] = $this->parser->evaluate($expression, $context);
                }
                $tokens[] = new SassScriptFunction($matches[SassScriptFunction::NAME], $args);
            } elseif (($match = SassBoolean::isa($string)) !== false) {
                $tokens[] = new SassBoolean($match);
            } elseif (($match = SassColour::isa($string)) !== false) {
                $tokens[] = new SassColour($match);
            } elseif (($match = SassNumber::isa($string)) !== false) {
                $tokens[] = new SassNumber($match);
            } elseif (($match = SassString::isa($string)) !== false) {
                $stringed = new SassString($match);
                if (strlen($stringed->quote) == 0 && SassList::isa($string) !== false) {
                    $tokens[] = new SassList($string);
                } else {
                    $tokens[] = $stringed;
                }
            } elseif (($match = SassScriptOperation::isa($string)) !== false) {
                $tokens[] = new SassScriptOperation($match);
            } elseif (($match = SassScriptVariable::isa($string)) !== false) {
                $tokens[] = new SassScriptVariable($match);
            } else {
                $_string = $string;
                $match = '';
                while (strlen($_string) && !$this->isWhitespace($_string)) {
                    foreach (SassScriptOperation::$inStrOperators as $operator) {
                        if (substr($_string, 0, strlen($operator)) == $operator) {
                            break 2;
                        }
                    }
                    $match .= $_string[0];
                    $_string = substr($_string, 1);
                }
                $tokens[] = new SassString($match);
            }
            $string = substr($string, strlen($match));
        }
        return $tokens;
    }

    /**
     * Returns a value indicating if a token of this type can be matched at
     * the start of the subject string.
     * @param string the subject string
     * @return mixed match at the start of the string or false if no match
     */
    public function isWhitespace($subject)
    {
        return (preg_match(self::MATCH_WHITESPACE, $subject, $matches) ? $matches[0] : false);
    }

}
